Resilient biodegradable packaging materials

ABSTRACT

Biodegradable starch-based extruded products and methods of manufacturing those products are provided. In particular, extruded starch products processed by compression, stretching or compression and stretching provide excellent flexibility, pliability, dimensional stability, resiliency, abrasion resistance and other properties making them attractive for use as packaging materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 08/784,859, filed Jan. 15, 1997, which is acontinuation-in-part of U.S. patent application Ser. No. 08/421,720,filed Apr. 14, 1995 both of which are incorporated in their entirety byreference herein.

FIELD OF THE INVENTION

[0002] This invention relates generally to expanded biodegradablestarch-containing products with improved flexibility, pliability orresiliency and other properties appropriate for use as packagingmaterials, particularly for extruded sheets, molded trays and otherpackaging containers. The invention includes improved methods formanufacture of expanded starch products and starch-containing extruderfeed compositions.

BACKGROUND OF THE INVENTION

[0003] Biodegradable materials are presently in high demand forapplications in packaging materials. Commonly used polystyrene(“Styrofoam” (Trademark)), polypropylene, polyethylene, and othernon-biodegradable plastic-containing packaging materials are considereddetrimental to the environment. The use of such non-biodegradablematerials will decrease as government restrictions discourage their usein packaging applications. Biodegradable materials that are flexible,pliable and non-brittle are needed in a variety of packagingapplications, particularly for the manufacture of shaped biodegradablecontainers for food packaging.

[0004] For such applications, the biodegradable material must havemechanical properties that allow it to be formed into and hold thedesired container shape, being resistant to collapse, tearing orbreaking. In addition, biodegradable materials with resiliency,compressibility and bulk density comparable to “Styrofoam” (Trademark)“peanuts” are needed in loose-fill packaging applications. Further,biodegradable sheet materials having properties comparable topolypropylene and polyethylene materials are needed, for example, inlaminating packaging materials.

[0005] Starch is an abundant, inexpensive biodegradable polymer. Avariety of biodegradable starch-based materials have been proposed foruse in packaging applications. Conventional extrusion of starch producesexpanded products that are brittle, sensitive to water and unsuitablefor preparation of packaging materials. Attempts to prepare starch-basedproducts with flexibility, pliability or resiliency and other mechanicalproperties acceptable for various biodegradable packaging applicationshave generally focused on chemical or physico-chemical modification ofstarch, the use of expensive high amylose starch or mixing starch withsynthetic polymers to achieve the desired properties while retainingbiodegradability. A number of references relate to extrusion, andinjection molding of starch-containing compositions.

[0006] U.S. Pat. Nos. 4,133,784, 4,337,181, 4,454,268, 5,322,866,5,362,778, and 5,384,170 relate to starch-based films that are made byextrusion of destructurized or gelatinized starch combined withsynthetic polymeric materials. U.S. Pat. No. 5,322,866 specificallyconcerns a method of manufacture of biodegradable starch-containingblown films that includes a step of extrusion of a mixture of rawunprocessed starch, copolymers including polyvinyl alcohol, a nucleatingagent and a plasticizer. The process is said to avoid the need forpre-processing of the starch. U.S. Pat. No. 5,409,973 reportsbiodegradable compositions made by extrusion from destructurized starchand an ethylene-vinyl acetate copolymer.

[0007] U.S. Pat. No. 5,087,650 relates to injection-molding of mixturesof graft polymers and starch to produce partially biodegradable productswith acceptable elasticity and water stability. U.S. Pat. No. 5,258,430relates to the production of biodegradable articles from destructurizedstarch and chemically-modified polymers, including chemically-modifiedpolyvinyl alcohol. The articles made are said to have improvedbiodegradability, but to retain the mechanical properties of articlesmade from the polymer alone. U.S. Pat. No. 5,292,782 relates to extrudedor molded biodegradable articles prepared from mixtures of starch, athermoplastic polymer and certain plasticizers. U.S. Pat. No. 5,403,875relates to blends of starch with acrylic polymers which aremelt-processed into thermoplastic articles. U.S. Pat. No. 5,393,804relates to biodegradable compositions made from starch melts containingconverted starch and plasticizers including polyvinyl alcohol. U.S. Pat.No. 5,095,054 concerns methods of manufacturing shaped articles from amixture of destructurized starch and a polymer.

[0008] U.S. Pat. No. 4,125,495 relates to a process for manufacture ofmeat trays from biodegradable starch compositions. Starch granules arechemically modified, for example with a silicone reagent, blended withpolymer or copolymer and shaped to form a biodegradable shallow tray.

[0009] U.S. Pat. No. 4,673,438 relates to extrusion and injectionmolding of starch for the manufacture of capsules. U.S. Pat. No.5,427,614 also relates to a method of injection molding in which anon-modified starch is combined with a lubricant, texturizing agent anda melt-flow accelerator.

[0010] U.S. Pat. Nos. 4,863,655, 5,035,930 and 5,043,196 report expandedstarch materials in which the starch has at least 456% by weight amylose(high amylose materials). Expanded high amylose starch compositions havealso been modified by reaction with oxiranes (e.g. ethylene oxide) andinclude the commercially available “ECO-FOAM” (Trademark) in which thestarch is modified by reaction with propylene oxide. Expanded packagingmaterials made from high amylose starch are too expensive for practicalcommercial use. U.S. Pat. No. 5,314,754 of Knight (May 24, 1994) reportsthe production of shaped articles from high amylose starch.

[0011] EP published application EP 712883 (published May 22, 1996)relates to biodegradable, structured shaped products with goodflexibility made by extruding starch having defined large particle size(e.g., 400 to 1500 microns). The application, however, only exemplifiesthe use of high amylose starch and chemically-modified high amylosestarch.

[0012] U.S. Pat. No. 5,512,090 refers to an extrusion process formanufacture of resilient, low density biodegradable packaging materials,including loose-fill materials, by extrusion of starch mixturescomprising polyvinyl alcohol (PVA) and other ingredients. The patentrefers to a minimum amount of about 5% by weight of PVA. U.S. Pat. No.5,186,990 reports a lightweight biodegradable packaging materialproduced by extrusion of corn grit mixed with a binding agent (guar gum)and water. Corn grit is said to contain among other components starch(76-80%), water (12.5-14%), protein (6.5-8%) and fat (0.5-1%).

[0013] U.S. Pat. No. 5,208,267 reports biodegradable, compressible andresilient starch-based packaging fillers with high volumes and lowweights. The products are formed by extrusion of a blend of non-modifiedstarch with polyalkylene glycol or certain derivatives thereof and abubble-nucleating agent, such as silicon dioxide. U.S. Pat. No.5,252,271 of Hyrum (Oct. 12, 1993) reports a biodegradable closed celllight weight packaging material formed by extrusion of a modifiedstarch. Non-modified starch is reacted in an extruder with certain mildacids in the presence of water and a carbonate compound to generate CO₂.Resiliency of the product is said to be 60% to 85%, with density lessthan 0.032 g/cm³.

[0014] U.S. Pat. No. 3,137,592 relates to gelatinized starch productsuseful for coating applications produced by intense mechanical workingof starch/plasticizer mixtures in an extruder. Related coating mixturesare reported in U.S. Pat. No. 5,032,337 to be manufactured by extrusionof mixture of starch and polyvinyl alcohol. Application ofthermomechanical treatment in an extruder modifies the solubilityproperties of the resultant mixture which can then used as a bindingagent for coating paper.

[0015] While significant progress has been made toward non-brittle,starch-based biodegradable packaging materials, there neverthelessremains a significant need for lowering production costs and improvingthe physical and mechanical properties of extruded starch materials.

SUMMARY OF THE INVENTION

[0016] The present invention provides methods for producingbiodegradable expanded starch products with improved properties forpackaging applications. These methods comprise the steps of extruding astarch-containing mixture through an expansion die, followed bycompressing the extrudate, for example, by subjecting the extrudate topressure generally perpendicular to the direction of extrusion.Compression can be applied, for example, by use of a rolling device. Theextrusion can be performed using conventional methods and apparatus. Diesize, die shape and/or type of compression used, e.g., rollerconfiguration, are selected to produce a shaped, compressed or rolledextrudate. The compressed or rolled exudate is optionally subjected tofurther shaping, molding and/or cutting to obtain a desired final shapedarticle to suit the planned application.

[0017] It has been found that compressing, or compression combined withstretching of the starch-based extrudate significantly improves theflexibility, pliability, mechanical strength and dimensional stabilityof extruded, pressure molded packaging containers. The preferred methodfor compression of the extrudate is by rolling. It has also been foundthat compression or rolling improves the resiliency of extruded, lowdensity expanded starch articles, such as those useful for loose fillapplications. Significant decreases in the brittleness of extrudedstarch products are achieved by compressing, rolling, compressing andstretching or rolling and stretching of the material after extrusion.Application of the methods of this invention allows production ofexpanded starch packaging materials having mechanical propertiessuitable for packaging application using significantly lower levels ofexpensive polymeric plasticizers, e.g., polyols such as polyvinylalcohol.

[0018] In the method of this invention, pressure can be applied to theemerging extrudate in a direction generally perpendicular to thedirection of extrusion. Pressure is preferably applied substantiallyperpendicular to the direction of extrusion. The pressure applied ispreferably sufficient to substantially compress the cells in theextrudate. Surprisingly, it is believed that substantially compressing,or preferably crushing, the cells of the expanded product significantlyimproves the flexibility, pliability or resiliency of the product andsignificantly reduces brittleness. The preferred method of applyingpressure to the extrudate is rolling the extrudate between opposedrollers. The amount of pressure applied may be varied dependent upon thedesired final properties of the material. Rolling is preferably donewhile the extrudate is still hot, most preferably immediately upon exitof the extrudate from the extruder die.

[0019] In another aspect, the present invention provides a method ofproducing improved expanded starch products comprising the steps ofextruding a starch-containing mixture through an expansion die, followedby stretching the extrudate, for example, by pulling the extrudate inthe direction of extrusion. Stretching can be applied, for example, bypulling the extrudate strand, substantially in the direction ofextrusion, faster than the rate of extrusion. Extrusion can be performedusing conventional methods and apparatus. Die size, die shape and/orstretching rate applied are adjusted to provide desired final propertiesin the extruded product. The stretched extrudate is optionally subjectedto further shaping, molding and/or cutting to obtain a desired finalshaped article to suit the planned application. Stretching of thestarch-based extrudate significantly improves the final properties ofshaped extruded articles, including pressure molded packagingcontainers.

[0020] In one embodiment of the method, the extrudate is compresseswithout substantial stretching. The preferred way to achieve compressionwithout substantial stretching is to employ rollers in which rollerspeed is substantially matched to the rate of extrusion, so that minimallateral pressure is applied to stretch the extrudate. In anotherembodiment of the method, the extrudate is stretched, for example bypulling the extrudate strand as it exits the die at rate faster than theextrusion rate. Preferred stretch rates range from about 1.1 to about1.5.

[0021] In yet another embodiment, the extrudate is compressed andstretched. The extrudate can be stretched before, after or at the sameit is being compressed. Preferably stretching is applied at the sametime as compression. The preferred way to compress and stretch theextrudate is to employ rollers in which the roller speed is set fasterthan the rate of extrusion. In this case, the extrudate is both rolledand stretched. Roller speeds for stretching are typically set to be lessthan or equal to 50% faster than the extrusion rate. Preferred rollerspeeds for stretching are between about 10% to about 20% faster than theextrusion rate. However, the desired amount of stretching is dependentupon the desired final properties of the product as used herein, aroller speed of 10%, 20%, or 50% faster than the extrusion rate means a1.1, 1.2 or a 1.5 stretch rate of the extrudate, respectively.

[0022] The compressed, stretched, compressed and stretched expandedstarch product is biodegradable and has low brittleness and otherproperties making it attractive for use in packaging applications.

[0023] In one embodiment, this invention provides improved starch sheetsfor cushioning and packaging applications. Sheets are preferablyprepared by rolling, or rolling and stretching the extrudate, using aflat roller. Rolled expanded starch sheets are generally useful inpackaging and wrapping applications and in the manufacture of laminatedmaterials for packaging applications, such as for manufacture of mailingenvelopes and related containers. Single-ply, two-ply or multiple plysheets can be formed by the method of this invention.

[0024] In another embodiment, this invention provides improved moldedstarch articles, particularly articles that are pressure molded fromextruded compressed, rolled or rolled and stretched starch sheets.Molded articles can have various sizes and shapes including shallow anddeep trays, cups, tubs, tubes and other containers. Molded articles canalso be single or multiple compartment trays or containers and can alsobe shaped with internal or external ridges, lips, or rims. The starchextrudate is compressed, rolled, or rolled and stretched prior topressure molding. Pressure molding can employ conventional processes andequipment.

[0025] In yet another embodiment, this invention provides improvedexpanded starch materials having high resiliency, suitablecompressibility, low density, low dusting, and low brittleness for usein loose fill packaging applications. These improved starch materialsare produced by methods described herein by extrusion, combined with astep of compressing or substantially crushing the cells in theextrudate, preferably by rolling the hot extrudate. Loose-fill can beproduced in a variety of shapes by choice of suitable combinations ofdie and roller shapes. This invention provides a loose fill expandedstarch product with resiliency higher than 50% useful for packagingapplications. Loose-fill products of this invention havecompressibility, flexibility properties comparable to “Styrofoam” loosefill.

[0026] The methods of this invention can be employed essentially withany starch composition suitable for extrusion. In particular andpreferably, the method can be used with starch compositions in which themajor ingredient is raw non-modified starch. The method of thisinvention allows the use of significantly lower levels of plasticizersin the starch extruder feed than previously known to achieve desiredmechanical properties in the final expanded or molded starch products.

[0027] The invention also provides extruder feed mixtures containingraw, non-modified starch for production of expanded starch productswhich contain lower levels of plasticizers, particularly lower levels ofpolymeric plasticizers, such as PVA and related polyols. Extruder feedmixtures of this invention may comprise non-modified starch. To achievelower production costs, extruder feed mixtures preferably contain lessthan 5% (by weight) PVA or related polyhydric plasticizer. Morepreferred extruder feed mixtures contain less than or equal to about2.5% PVA or related polyhydric plasticizer. Most preferred extruder feedmixtures contain no PVA or related polyhydric plasticizer.

[0028] It has been found that lighter weight expanded starch articlesand expanded starch pressure molded articles with good mechanicalstrength and dimensional stability can be produced by the process ofthis invention from extruder feed mixtures that contain talc.

[0029] In another aspect, the invention provides a new extrusion devicein which a conventional extruder is combined with a pressure devicewhich can apply pressure to an extrudate emerging from an extruder diesubstantially perpendicular to the direction of extrusion. The pressureapplied being sufficient to substantially compress or preferably tocrush the cells in the hot extrudate. The amount of pressure applied andthe length of application time of pressure depends upon the desiredfinal properties of the product.

[0030] Additional aspects and features of the invention will becomeapparent in the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a schematic drawing of an extrusion/rolling orextrusion/rolling and stretching device useful in practicing the methodsof this invention.

[0032]FIG. 2 is a schematic drawing of a flow smoother employed in thedevice of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The process of making shaped extruded starch articles of thisinvention is described by reference to the schematic manufacturingextrusion apparatus of FIG. 1. Raw non-modified starch is mixed withdesired additives, for example in an attached feeder (1), through a feedtube (2) and introduced into the mixing compartment of an extruder (3),preferably a twin screw extruder, for example through an inlet (4). Thefeed tube (2) contains a flow smoother (5). The mixture is further mixedand blended, subjected to shearing, increasing temperature and pressurein the extruder to form a mass which is forced through an expanding die(7). The mass is preferably a homogeneous hot melt. Preferably, the massis plasticized.

[0034] As shown in more detail in FIG. 2, the feed tube (2) of thefeeder (1) contains a flow smoother (5). This device functions to ensureconsistent feed to the extruder to minimize or prevent surging of feedinto the extruder. The device comprises arms or spokes (6) that traversethe mouth of the feed tube. Most simply, the device can comprise a setof crossed wires secured at and across the mouth of the feed tube. Otherconfigurations of the flow smoother will be readily apparent to those ofordinary skill in the art. It has been found that the quality of theextruded material, particularly the quality of extruded sheets issignificantly improved, if a flow smoother is employed.

[0035] The shape of the die determines the shape of the extruded strandand die shape is typically chosen to prepare a desired shape of expandedproduct. The mixture is typically extruded out of the die at a pressureof about 700 to 2000 psi and the extrudate is at a temperature of about120° C. to about 200° C. at extrusion. The extruder is typically heatedand can have several zones along its length in which temperature isseparately adjustable.

[0036] For preparation of pressure molded expanded starch articles,including trays, the extrudate is preferably formed as a tube by use ofan annular or tubular extruder die. The thickness of the extruded tubeis preferably between about 0.1 and 0.05 inches and more preferablybetween about 0.1 to 0.03 inches. The extruder tube produced ispreferably immediately compressed, e.g., by rolling or rolling andstretching, between a pair of flat opposed rollers. Rolling of the tuberesults in a two-ply sheet. Multi-ply sheets can be formed by overlayingtwo or more extruded tubes followed by compression or rolling.Alternatively, the extruded tube can be split to form a strip which isthen compressed or rolled to give a single-ply sheet. The compressed orrolled sheet is optionally cut, and further shaped. For example, arolled sheet can be passed into a pressure mold where it is pressed intothe shape of the desired product. The resulting shaped article can befinished by smoothing or trimming rough edges or by the application ofdesired coatings. For example, sealants, lubricants, water-resistant orwater-repellant coatings can be applied to achieve a desired surfaceappearance or quality or to minimize loss of water from (or absorptionof excess water by) the shaped article. Dyes, fragrances, preservatives,bactericides may also be included or added into the extrudate used toform a shaped article.

[0037] The term sheet is used herein to refer to a generally flat,relatively thin slab of extrudate which is preferably sufficiently thickto allow formation of an expanded starch article which retainsdimensional stability. A sheet as used herein is not intended to includefilms which do not retain dimensional stability. The method of thisinvention can be employed to make films, however, sheets are thepreferred precursor to shaped extruded molded articles. Preferred sheetsfor preparation of extruded starch articles have thickness that isgreater than about {fraction (1/50)}th of an inch and more preferablygreater than about {fraction (1/16)}th of an inch. In general, however,the thickness of the sheet, which is determined in part by choice of dieand type of compression or stretching applied, e.g., roller gap, isselected to achieve desired final dimensions and properties in theshaped extruded starch article.

[0038] It has been found to be beneficial to the quality of the finalmolded product to pinch the ends of the extruded tube prior tocompression or rolling. It is believed that pinching the tube end toform a pillow entraps steam that is beneficial during thecompression/rolling process to better maintain the temperature ofextrudate on compression/rolling or to provide a humid environment forcompression/rolling. Provision of a steam box at the end of the extruderto enclose the extrudate as it is passed from the extruder die forcompression, e.g., as it is passed to the roller, will provide similarbenefit to the quality of the compressed or rolled material. It has beenfound that the length of time between rolling and molding has asignificant effect on the quality of the resultant molded article.Preferably the compressed or rolled sheet is immediately passed to themold for pressure molding. It is believed that an important factor inthis step is the temperature of the mold in relation to the temperatureof the sheet. The sheet is preferably pressure molded while still hot.Alternatively, the mold itself can be heated to insure consistentquality of product.

[0039] Water can be added to the extrusion system during the residenceof the base starch mixture in the extruder to adjust the consistency ofthe starch mixture during extrusion and/or to adjust the extent ofexpansion of the product. Lubricant levels in the extrudate can also beadjusted to improve flow through the extruder. Glycerin levels in theextruder can also be adjusted to improve flow and/or vary properties ofthe expanded product. There is no requirement to remove water from thebase mixture in the extruder prior to extrusion. Specifically, there isno requirement to apply subatmospheric pressure to the extrudate orextruded strand to remove water.

[0040] Continuing to refer to FIG. 1, the extrudate strand which exitsthe die (7) is preferably fed through a rolling device (10) having twoor more rollers (11) positioned with respect to each other to applypressure to the strand substantially perpendicular to the direction ofextrusion. Multiple set of rollers can be employed, positionedsequentially along the direction of extrusion to sequentially applypressure to the extrudate. Pressure from each roller employed ispreferably applied substantially perpendicular to the direction ofextrusion. Each set of rollers can be set to apply the same or differentamounts of pressure to the extrudate. The rollers in a given set ofrollers can form an opening corresponding to the shape of the desiredproduct. For formation of expanded starch sheets, including those whichare subsequently optionally pressure molded, one or more pairs ofopposed flat rollers can be employed. Preferably, the rollers exertsufficient pressure upon the strand to substantially compress the cells,or more preferably crush the cells, in the strand. The rollers can alsobe used to finalize shaping of the expanded product.

[0041] The process step of applying pressure to the extrudate strand,preferably by rolling, is an important improvement in the manufacturingprocess of this invention which results in significantly decreasedbrittleness of extruded starch products. The application of pressure asdescribed herein also reduces dustiness and chipping of extrudedproducts and increases bulk density. The roller pressure required toobtain improved properties depends on the shape of the extrudate, cellsize and bulk density of the extrudate which in turn depends on thecomposition of the extrudate including the type of starch and watercontent. The required roller pressure needed to achieve the desiredfinal properties is readily determined for a particular starchcomposition and product shape empirically without the expense of undueexperimentation. In general, roller pressure for making sheet productswill be higher than in making shaped loose fill.

[0042] Roller speed can be adjusted to substantially match the extrusionrate. If this is done, minimal stretching of extrudate occurs.Alternatively, the roller speed can be adjusted to be somewhat fasterthan the rate of extrusion. In this case, the extrudate is both rolledand stretched. compression accompanied by stretching, as applied when anextrudate is rolled and stretched, has surprisingly been found to conferimproved properties on starch articles molded using the compressed andstretched extrudate. Roller speeds up to about 50% faster than theextrusion speed can be applied to achieve stretching with compression.Preferred roller speeds for stretching and compression are between about10% to about 20% faster than the rate of extrusion.

[0043] The substantially compressed or preferably crushed extrudate iscut into desired lengths by a cutting device, for example with arotating knife positioned after the rollers. For preparation of loosefill, the resultant cut strands are preferably cured under controlledtemperature and humidity conditions. Loose fill curing is preferablydone between 18°-30° C., and more preferably at about 21° C., athumidity ranging from about 40%- about 80%, and more preferably at about50% humidity, for about 1 or 2 days.

[0044] The manufacture of expanded starch loose fill and expanded starchsheets is typically done in a continuous mode by continuous feed intothe extruder, extrusion, compression/rolling and cutting.

[0045] A conventional twin screw extruder having feed screws, singlelead screws, shear paddles (preferably 3 or more, 3-10 being typical)and mixing paddles (typically 1-5) can be employed in this process. Anexpanding type screw configuration can be used in the twin-screwextruder. Typical residence time of the base mixture (i.e. the starchwith any additives) in the extruder is from about 9 to about 20 secondsand extrusion occurs at a rate from about 100 to about 200 lb/h per dieinsert.

[0046] The size and configuration of the die opening determines thecross-sectional shape of the extrudate strand. A variety of shapes andsizes of final products can be made. The starch can also be extruded asan expanded sheet to make sheets of cushioning material or for furthershaping through pressure molding. Typically, product sheets having athickness of about {fraction (1/10)} to about ¼ inch can be made by theextrusion/compression method. Extruded starch products for loose fillpackaging material, for example, can have several cross-sectionalshapes, including among others, capital omicron, FIG. 8, short rods,S-shaped, C-shaped, oval, and an omega. The product shape does notsignificantly effect resiliency of loose fill packing material. Bulkdensity of loose fill can, however, be dependent upon shape.

[0047] A preferred rolling device applies pressure to the extrudatestrand substantially perpendicular to the direction of extrusion. Thehot extrudate strand can simply be passed through opposed flat rollers(which may distort the shape imposed by the die). Generally, it ispreferred that the roller or rollers apply pressure symmetrically to thehot extrudate conforming to the desired product shape, e.g., a rolledsheet is preferably employed for pressure molding of trays and likecontainers. Rollers can be made of stainless steel, teflon or a relatedmaterials that are inert to the extrudate. Rollers are preferablypositioned with respect to the extruder die such that the hot extrudatestrand can be directly fed into the rollers while the extrudate strandis still hot.

[0048] A compression or rolling step has not previously been applied tothe production of expanded starch products. Preferred rollers arespring-loaded and the pressure applied is adjustable. While rolling isthe preferred method for applying pressure to the extruded strand toachieve desired properties in expanded starch articles, those ofordinary skill in the art will appreciate that other methods may beapplied to achieve the desired result. It will also be appreciated thata variety of methods are available to stretch the extrudate. Inparticular, a variety of methods are available for stretching theextrudate before, during or after compression.

[0049] Preferably, rollers are positioned sufficiently close to theextruder die so that the extrudate remains hot during rolling. For easeof illustration, the roller device of FIG. 1 shows one set of rollers.Two or more sets of rollers in sequence can be employed in theprocessing method of this invention. The use of more than one set ofrollers may improve process efficiency. However, care should be taken tokeep the extrudate hot during the process of rolling. Rollers may beheated. For production of starch sheets, in particular, the use of twoor more rollers may be preferably to achieve desired final properties.

[0050] The shape of loose fill packaging material affects theinterlocking capability of the material. Loose fill shaped so that thereis some interlocking between pieces is less readily displaced byjostling and better protects packaged items from impact damage. Loosefill shapes preferred for interlocking capability are those withprotrusions or indentations which allow pieces to interlock.

[0051] The preferred extruder feed compositions of this inventioncontain raw non-modified starch as a major ingredient (about 70% toabout 97% by weight). Minor amounts of additives, including lubricant,plasticizer, humectant, nucleating agent and another blowing agent (inaddition to water) wherein the additives preferably comprise up to amaximum of 30% by weight of the total weight of the extrudates, may beadded. One of the preferred extrudates contains a minimum amount ofplasticizers, including polyvinyl alcohol or ethylene vinyl alcohol (orother polyols) to obtain desired properties when processed by theimproved extrusion/compression method described herein. In particular,preferred extruder feed contains less than about 5% by weight ofpolyvinyl alcohol or ethylene vinyl alcohol. More preferred extruderfeeds contain less than or equal to about 2.5% by weight or contain lessthan or equal to about 1% by weight of polyvinyl alcohol or ethylenevinyl alcohol.

[0052] Water is typically added to the extruder feed during its passagethrough the extruder, most typically at the inlet portion of theextruded. Added water may generally represent about 30% or less of thestarch composition in the extruder. Additional variable amounts of waterare present in the starch itself. The amount of water added in a givenextrusion will depend on the extrusion conditions, the initial watercontent of the starch used and the desired product. Generally, theamount of water in the extrudate is adjusted to maximize expansion ofthe extruded product, while avoiding a soft or runny extrudate. Watercan be premixed with or added separately from other base starch mixtureingredients. For example, water can be added, and its addition adjustedand controlled, through inlet ports into the extruder. The amount ofwater that must be added depends on the moisture content of the rawstarch. The total water content of the base starch mixture prior toextrusion is typically between about 6% and about 18%.

[0053] It has been found that pressure molded articles having suitableproperties for packaging applications, such as containers and trays, canbe prepared using extruder feed compositions which contain no polymericor polyol plasticizer, e.g., no PVA or EVA.

[0054] In preferred embodiments, this invention uses raw, non-modified,non-derivatized starch which is essentially starch as it occurs innature other than having been physically separated from other plantcomponents. The starch is typically a powder (fine or coarse) orgranular. Cornstarch is the preferred starch in this invention, howeverany type of non-modified starch from wheat, rice, potatoes, tapioca, orthe like or mixtures of starches can also be used. Mixtures of starchesfrom different plant sources can be employed. In addition, other naturalor synthetic materials that comprise starch as a major component, forexample rice flour, can also be used as the source of starch for theprocess of this invention.

[0055] The invention does not require the use of high amylose starch toachieve desired high flexibility or resiliency. The invention does notrequire the use of derivatized starch, such as starch which has beenchemically reacted at the hydroxy groups (e.g. esterified, etherified orphosphorylated). The invention does not require preconditioning ofstarch by treatment with heat or pressure, gelatinization ordestructurization of starch before addition to the extruder.Nevertheless, starch compositions comprising high amylose starch,modified or derivatized starch or starch compositions that arepreconditioned, gelatinized or destructurized can be processed by theimproved extrusion/compression or and compression and stretching processof this invention to provide extruded materials with improved propertiesfor use as packaging materials. Mixtures of modified or otherwisetreated starch and raw, non-modified starch can be employed in themethods of this invention. Preferred starch for use in this invention ispredominantly non-modified starch, i.e. starch containing 50% or more byweight non-modified starch.

[0056] Flexible, pliable or resilient expanded starch products of thisinvention can be prepared with lower levels of plasticizers,particularly polyvinyl alcohol, ethylene vinyl alcohol and relatedpolyol materials than has been taught in the prior art.

[0057] The pre-mixed base starch mixture, the extruder feed (includingany added water, lubricant, glycerin or other ingredient) can bedirectly introduced into the extruder or the individual components canbe added in any order into the extruder for mixing therein. In apreferred method of addition of the components, water, lubricant andglycerin are added to the remaining ingredients in the extruder throughindependently adjustable inlets into the extruder. Extruder feedmixtures of this invention predominantly comprise starch with minoramounts of nucleating agent, such as corn meal or talc.

[0058] The preferred extruder feed mixture of this inventionpredominantly comprise starch with minor amounts of humectants,plasticizers, lubricants, nucleating agents and optional blowing agentsand agents which function to reduce cell size. Glycerin, related polyolsincluding pentaerythritol, and vegetable oil among others may functionin starch extrusion as humectants and/or lubricants to improve the flowproperties of the mixture and provide smooth surfaces for extrusion.Polyvinyl alcohol, ethylene vinyl alcohol and related polymeric polyolsmay function as plasticizers. Glycerin may also function as aplasticizer. Talc, protein as grain meal, in egg albumin or blood mealor other protein sources, and materials which generate CO₂-like“Hydrocerol” (Trademark, Boehringer Ingelheim) may function asnucleating agents.

[0059] Encapsulated sodium bicarbonate and citric acid mixtures forexample, Myvaplex, which generates CO₂ and sodium citrate, for example,“Hydrocerol” (CF and BIH forms, for example, available from BoehringerIngelheim) can act as a nucleating agent. Different forms ofencapsulated material are available in which the encapsulatedingredients are released at different temperatures. Those of ordinaryskill in the art can readily choose the appropriate form for a givenapplication. In general, the form which releases at the lowesttemperature compatible with the application is used. Glycerolmonostearate and other glycerol monoesters of fatty acids may functionto aid in formation of uniform small cells in the extruded material.Superheated water in the extrudate may act as a blowing agent. Theextruder feed of this invention can also include additional minoramounts of blowing agents, including among others carbonate saltsincluding sodium, potassium and ammonium salts. Any vegetable oils orpolyols employed in the base mixture are preferably pumpable. Ingeneral, the extruder feed mixture of this invention may containcombinations of one or more humectants, plasticizers, lubricants,nucleating agents and/or blowing agents. The maximum amount of theseadditives is preferably about 30% by weight of the total weight of theextruder feed mixture (including added water). The extruder feed mixturepreferably contains a minimum of these additives needed to attaindesired properties of extruded product. The base mixture contains aminimum amount of plasticizer to decrease its cost. Thecompression/rolling step of this invention allows the use of much loweramounts of plasticizers than are required in prior art processes toobtain flexible, non-brittle expanded starch products. Preferredextruder feed contain less than about 5% plasticizer. Polymeric vinylalcohols are often employed in starch extrusion processes asplasticizers. The preferred extruder feed mixtures of this inventioncontain less than about 5% by weight of polyvinyl alcohol, polyethylenealcohol or related polymeric vinyl alcohols (or mixtures thereof).Preferred extruder feed mixtures of this invention include those inwhich the amount of polymeric vinyl alcohol is less than about 5% byweight and, specifically, those having less than about 2.5% by weight aswell as those having less than about 1% by weight of polymeric vinylalcohol. PVA having different average molecular weights, is available.Airol 325 and Airol 540, both available from Air Products were foundsuitable in extruder feeds of this invention. Mixtures of this inventionmay also contain relatively low levels of glycerin or other humectants.Mixtures of this invention include those in which glycerin content isless than about 1.5% by weight and those in which glycerin content isless than about 0.5% by weight. Mixtures of this invention also includethose in which talc content is between about 1% by weight to about 10%by weight and those in which talc content is between about 1% by weightand about 5% by weight.

[0060] Glycerol monostearate (for example, “Myvaplex” (Trademark,Eastman Kodak) can be included in the extruder feed to provide improveduniformity of cell size in the expanded starch. Glycerol monostearate ispreferably included in the extruder feed in an amount ranging from about0.1% to about 0.5% by weight. More preferably, it is present in anamount from about 0.15% to about 0.25% by weight.

[0061] For example, extruder feed mixture of this invention can containthe following ingredients expressed in weight percent: starch (about 70%to about 97%), preferably predominantly raw, unmodified starch; addedwater (up to about 30%); vegetable oil (up to about 6%); glycerin (up toabout 3%); polyvinyl alcohol or other plasticizer (up to about 25%,preferred maximum of less than about 5%); proteinaceous grain meal (upto about 20%); glycerol monostearate (up to about 0.5%); additionalblowing agent (up to about 0.8%); and talc (up to about 10%) with theprovision that the mixture must contain a nucleating agent. Additionalwater and/or lubricant can be added during extrusion.

[0062] Other examples of extruder feed mixtures suitable for use in thisinvention include the following where composition is expressed in weightpercent:

[0063] Composition A comprising:

[0064] Starch about 60% to about 97%;

[0065] Proteinaceous grain meal 0% to about 10%, if present, preferablyabout 4% to about 10%;

[0066] Polyvinyl alcohol 0% to about 27%, if present, preferably lessthan about 5%;

[0067] Talc 0% to about 20%, if present, preferably about 0.1% to about10%, more preferably about 0.1% to about 1.5%;

[0068] “Myvaplex” (Glycerol monostearate) 0% to about 0.5%, if present,preferably about 0.1% to about 0.3%, more preferably about and 0.2%;

[0069] “Hydrocerol” 0% to about 2%, if present, preferably about 0.2% toabout 0.5%;

[0070] with the proviso that a nucleating agent must be present;

[0071] Composition B comprising:

[0072] Starch about 70% to about 97%;

[0073] Proteinaceous grain meal preferably about 4% to about 10%;

[0074] Polyvinyl alcohol 0% or if present, preferably less than about5%, more preferably less than about 2.5% or less than about 1%;

[0075] Talc 0% or if present preferably about 0.1% to about 1.5%;

[0076] “Myvaplex” about 0.2%; and

[0077] “Hydrocerol” 0% or is present preferably about 0.2% to about0.5%;

[0078] Composition C comprising:

[0079] Starch about 70% to about 97%;

[0080] Proteinaceous grain meal 0% or if present preferably about 4% toabout 10%;

[0081] Polyvinyl alcohol preferably less than about 5%, more preferablyless than about 2.5% or less than about 1%;

[0082] Talc preferably about 0.1% to about 1.5%;

[0083] “Myvaplex” about 0.2%; and

[0084] “Hydrocerol” preferably about 0.2% to about 0.5%

[0085] Composition D comprising:

[0086] Starch about 70% to about 97%;

[0087] Proteinaceous grain meal 0% or if present preferably about 4% toabout 10%;

[0088] Polyvinyl alcohol preferably less than about 5%, more preferablyless than about 2.5% or less than about 1%;

[0089] Talc preferably about 0.1% to about 10%;

[0090] “Myvaplex” about 0.2%; and

[0091] “Hydrocerol” 0%, or if present, preferably about 0.2% to about0.5%;

[0092] Composition E comprising:

[0093] Starch about 70% to about 97%;

[0094] Polyvinyl alcohol preferably less than about 5%, more preferablyless than about 2.5% or less than about 1%;

[0095] Talc preferably about 0.1% to about 10%; more preferably about 1%to about 10%;

[0096] “Myvaplex” about 0.2%; and

[0097] “Hydrocerol” 0%, or if present, preferably about 0.2% to about0.5%;

[0098] Composition F comprising:

[0099] Starch about 70% to about 97%;

[0100] Polyvinyl alcohol preferably less than about 5%, more preferablyless than about 2.5% or less than about 1%;

[0101] Talc preferably about 0.1% to about 10%; more preferably about 1%to about 10%; and

[0102] “Myvaplex” about 0.2%;

[0103] Composition G comprising:

[0104] Starch about 70% to about 97%;

[0105] Talc preferably about 1% to about 10%, more preferably about 5%to about 6%; and

[0106] “Myvaplex” about 0.2%; and

[0107] “Hydrocerol” preferably about 0.2% to about 0.5%;

[0108] Composition H comprising:

[0109] Starch about 70% to about 97%;

[0110] Polyvinyl alcohol preferably less than about 5%, more preferablyless than about 2.5% or less than about 1%;

[0111] “Myvaplex” about 0.2%; and

[0112] “Hydrocerol” preferably about 0.2% to about 0.5%;

[0113] Composition I comprising:

[0114] Starch about 60% to about 97%;

[0115] Proteinaceous grain meal preferably about 4% to about 10%;

[0116] Polyvinyl alcohol up to about 27%;

[0117] “Myvaplex” about 0.2%;

[0118] Oil, e.g., vegetable oil, 0% to about 1.5%;

[0119] Glycerine 0% to about 1.5%; and

[0120] “Hydrocerol” preferably about 0.2% to about 1%;

[0121] The extruder feed composition of this invention can optionallycontain coloring agents, fragrances, bactericides and mould-inhibitingagents. The extruder feed may optionally include various sources offiber, e.g., soy fiber. Fiber content can preferably range up to about10% by weight of the extruder feed, but can be varied to adjuststiffness of extruded sheets and molded articles.

[0122] It has been found that starch materials that have been compressedinto sheets and pressure molded may be recycled back into the extrusionprocess by grinding the materials very finely, and combining them withadditional feed composition. For example, it has been found that the useof an extruder feed in which up to about 20% by weight of the starch isground recycled extruded starch results in no significant detriment toproperties of the final extruded, shaped product. Depending upon thedesired final properties of the product, a higher or lower percentage ofrecycled material may be included in the extruder feed for processing.

[0123] Resiliency (also called bulk resiliency) is the capability of amaterial to recover its size and shape, i.e. to recover its originalvolume, after deformation by a compressive force. Bulk resiliency of amaterial is assessed as percent recovery of volume by measuring theoriginal volume (as height of a given amount of material in a container)and the volume after about a 30-second recovery from the application ofa compressive force. The loose fill products made as described hereinwill generally have resiliency of about 50% or more. Preferred loosefill products will have resiliency over about 60%, and more preferredloose fill products will have resiliency of about 75% or more. Mostpreferred loose fill product will have resiliency between about 85% toabout 95%. In the present invention, high resiliency is substantiallyimparted to shaped expanded products by the physical processing step ofcompression, rolling, or preferably rolling with stretching of the hotextruded product. The minor amounts of humectants and plasticizers thatare included in the base starch mixture do not in themselves account forthe significant improvements in resiliency.

[0124] Packaging materials can also be compared and assessed based ontheir bulk density (weight/unit volume) and bulk compressibility (i.e.,the maximum force needed to compress the sample to a preselected % ofits original volume, typically to ⅔ of its original volume).Flexibility, the capability to bend without breaking, can be assessedqualitatively by applying hand pressure to the final extruded and moldedproducts squeezing to assess how much force can be applied before theextruded product breaks.

[0125] Compressed or rolled extrudates of this invention may have a bulkdensity less than about 2.0 lbs/ft³, but greater than 0.25 lbs/ft³. Thetypical bulk density for corn starch products of this invention is about0.5 to 0.8 lbs/ft³. The material as extruded is typically much lighterthan the final product since the compressing or rolling increases bulkdensity. Expanded starch products have moisture content generally lowerthan the extruder feed material. Typically, the compressed/rolledexpanded products contain from about 5% to about 9% by weight moistureand more typically from about 6% to about 7% by weight moisture.

[0126] The mechanical properties of pressure molded and other expandedstarch article made by the methods of this invention can be evaluated,for example, by preparation of tensile and Izod bars according to ASTMtest methods, D638-84 and D256-84.

[0127] The extruded expanded starch products of this invention areuseful in applications of shaped articles for packaging materials. Inaddition to loose fill packaging material, starch sheets for wrapping orother applications can be made by the extrusion/rolling method of thisinvention. In particular, starch sheets produced by methods herein canbe combined with paper and other biodegradable materials to makebiodegradable laminated materials, such as mailing envelopes. Further,articles having a variety of shapes including trays and other containerscan be produced by the methods herein combined with conventional methodsof molding, particularly pressure molding, of expanded starch.

[0128] The following examples are illustrative of this invention.

EXAMPLES Example 1 Preparation of Pressure Molded Expanded StarchProducts

[0129] Extruded starch sheets useful for pressure molding of trays andother shaped articles with low brittleness, suitable flexibility anduseful dimensional stability were prepared using the extrusioncompression method of this invention, exemplified by use of rollers toapply compression to the hot extrudate. Extruder feed compositionsuseful in this method include Compositions 1-I detailed above.

[0130] The components of the feed mixture were mixed prior to theirintroduction into the extruder. Water was added independently to theextruder. The extruder employed is a Wenger Model TX52 Twin-ScrewExtruder (Wenger Manufacturing, Inc. Sabetha, Kans.) which was adaptedwith feed screws, single lead screw, 5 shear paddles, and 10 mixingpaddles. The extruder barrel has three temperature zones. The mixture isplasticized in the extruder. In general, extruder conditions were set,as is known in the art, to provide smooth flow of extrudate. Moredetails provided below.

[0131] Screw Configurations

[0132] Standard (#1), high intensity (#2) or medium intensity (#3) screwconfigurations were suitable in extrusions.

[0133] Experimental conditions for the extrusion are:

[0134] Screw configuration (#1) has the following characteristics:  4 ea1.5 D  ¾ Pitch 10 ea Bilobal shear @ 45 deg  4 ea 1.5 D  ¾ Pitch  5 eaBilobal shear @ 45 deg  1 ea 376 cone screws

[0135] Screw configuration (#2) has the following characteristics:  4 ea1.5 D  ¾ Pitch 10 ea Bilobal shear @ 45 deg  2 ea 1.5 D  ¾ Pitch  1 ea1.5 D  ½ Pitch (cut flight)  1 set Circular shear locks, 6.5 mm thick(36/52 OD)  1 set Circular shear locks, 6.5 mm thick (42/47 OD)  8 eaBilobal shear @ 45 deg  1 set Circular shear locks, 13 mm thick (36/52OD)  1 ea 387 cone screws

[0136] Screw configuration (#3) has the following characteristics:  4 ea1.5 D  ¾ Pitch 10 ea Bilobal shear @ 45 deg  2 ea Bilobal shear (thin) 3 ea 1.5 D  ¾ Pitch  1 set Circular shear locks, 6.5 mm thick (42/47OD)  8 ea Bilobal shear @ 45 deg  1 set Circular shear locks, 13 mmthick (36/52 OD)  1 ea 387 cone screws

[0137] Run #1

[0138] The extruder feed (in weight percent) used was: raw, non-modifiedcorn starch 92.1%; PVA (Airvol 540) (Air Products) 2.4%); Talc 5.1%;“Myvaplex” 0.2%; and Hydrocerol BIH 0.3%.

[0139] Experimental Conditions for the Extrusion are

[0140] Screw configuration #1, Screw RPM 474 Tube Die (Assembly Dwg2979025A (BEI) die with adjustable outside die body, die body #2979025A,Mandrel #2979022A. Roller gap 0.203 mm. Roller speed 28 RPM (correspondsapproximately to feed rate to extruder (i.e., extrusion rate). Feed rate63 lb/hr. Temperatures Z4 180° Z3 100° Z2  70° Z1 120°

[0141] Water addition 0.21 lbs/min

[0142] Specific Mechanical Energy 0.099

[0143] The roller speed was set to correspond approximately to the feedrate so that sheets were rolled, but not stretched. Rolling improvedsheet quality and assured more uniform moisture content throughoutsheet. Increased flexibility from rolling was apparent. Good qualitytrays (flexible with dimensional stability) were produced in this run.

[0144] Run 2

[0145] The extruder feed (in weight percent) used was: raw, non-modifiedcorn starch 94.3%; talc 5.2%; “Myvaplex” 0.2%; and Hydrocerol BIH 0.3%;a feed that contains no PVA. The extruder conditions were:

[0146] Screw configuration #1, Screw RPM 500. Same die as in Run 1.Roller gap 0.203 mm. Roller speed 17 RPM. Feed rate 63 lb/hr.Temperatures Z4 180° Z3 100° Z2  70° Z1 136°

[0147] Water addition 0.25 lbs/min

[0148] Specific Mechanical Energy 0.087

[0149] Excellent Quality Trays were Made Using this Method

[0150] Run 3

[0151] This run employed the same feed as in Run 1 and was intended toevaluate the use of a higher feed rate and a high intensity screw. Thetrays made were excellent quality and no significant difference wasobserved for variation of parameters. Extruder conditions:

[0152] Screw configuration #2, Screw RPM 480. Same die as in Run 1.Roller gap 0.203 mm. Roller speed 17 RPM (sheet stretched and rolled.Feed rate 72.8 lb/hr. Temperatures Z4 180° Z3 100° Z2  70° Z1 153°

[0153] Water addition 0.32 lbs/min

[0154] Specific Mechanical Energy 0.11

[0155] Run 4

[0156] This run employed recycled extruded sheet (about 10% by weight ofthe total extrudate). The extruder feed (in weight percent) used was:total starch 92.1% (raw, non-modified cornstarch plus recycled extrudedstarch sheet, made using the formula of Run 1 above);PVA 2.4%; talc5.1%; “Myvaplex” 0.2% and Hydrocerol BIH 0.3%. Recycled extruded sheetis the remains of previous extruder test runs. The materials forrecycling were first flaked in a flaker and then ground three times to afine consistency in a Fitz mill. The ground material was blended withfresh material in a ribbon blender; the blend time was standard, about15 min. The trays made from feed containing recycled extruded sheet werepliable and had a silken feel. Extruder conditions:

[0157] Screw configuration #1, Screw RPM 500. Same die as in Run 1.Roller gap 0.203 mm. Roller speed 24 RPM. (Increased as feed rateincreased). Feed rate 63 lb/hr. (Increasing to 101 lbs/hr.) TemperaturesZ4 180° Z3 100° Z2  70° Z1 127°

[0158] Water addition 0.25 lbs/min

[0159] Specific Mechanical Energy 0.099

Example 2 Preparation of Loose Fill Packaging Material

[0160] A high resiliency (about 85% to about 95%) loose-fill packagingmaterial in the shape of a rod is prepared employing a base mixturehaving the following components listed as weight %: weight % unmodifiedcorn starch 77.7 water 2.8 vegetable oil 0.97 glycerin 1.6 polyvinylalcohol 4.9 corn meal 9.7 “Myvaplex” (Trademark, 0.39 Eastman Kodak,monoglyceride of stearic acid, i.e glycerol monostearate) talc 1.9

[0161] The corn starch employed had about 22 wt % amylose and about 8%to about 15% water by weight. The polyvinyl alcohol used had molecularweight range 200,000 to 300,000.

[0162] These ingredients, except water, vegetable oil and glycerine weremixed prior to introduction into the extruder. Water, vegetable oil andglycerine were added independently to the extruder through separateinlets. The extruder employed was a Wenger Model TX52 Twin-ScrewExtruder (Wenger Manufacturing, Inc. Sabetha, Kans.) which was adaptedwith feed screws, single lead screws, 5 shear paddles, 10 mixing paddlesand a 100 mil diameter die insert to produce a rod-shaped extrudate. Theextruder barrel had three temperature zones (150 Z6 [actual temperature144° C.], 90 Z5 [actual temperature 139° C.] and 70 Z4 [actualtemperature not measured]). The screw rpm was 495. The plasticized masswas extruded at a rate of 110 lb/h at 1000 psi and the extrudate was ata temperature of about 175° C. The residence time of the material in theextruder was about 13 seconds.

[0163] The extruded material was rolled perpendicular to the directionof extrusion to substantially compress the cells therein. Subsequent torolling, the stand can be cut into small approximately equal-lengthsegments (about 1 inch in length). The expanded, rolled and cut productswere cured at 21° C. in a 50% humidity for 24 h. The cured product hadexcellent resiliency and abrasion resistance.

Example 3 Laminated “Kraft” (Trademark) Paper for Packaging Applications

[0164] A base mixture of this invention is introduced into an extruder,such as the twin-screw extruder described in Example 1, adapted with aflat or slot die to form extruded sheets. The extruded sheets are rolledby rollers, preferably two sets of flat rollers, exerting pressureperpendicular to the extrusion direction and perpendicular to the planeof the sheet. The pressure exerted on the sheet was sufficient tosubstantially crush the cells in the sheet. The rolled sheet iscollected, if desired, by winding onto a roll and is cut along its widthto form desired sheet lengths. The rolled sheet material is cured atabout room temperature under medium humidity (about 40-60%).

[0165] The resulting pliable starch sheet can be directly employed inpackaging applications or can be used in laminated packaging products.Laminated packaging products include, among others, “Kraft” paperlaminated with pliable starch sheet.

[0166] “Kraft” paper is moistened with water, an appropriately sizedstarch sheet is positioned over the moistened paper and the layeredpaper and starch sheet are rolled to ensure overall contact and adhesionof the two layers. Additional layers of paper and or starch sheets canbe added by similar steps to obtain a multi-layer laminated material.“Kraft” paper with a single layer (about {fraction (1/10)}-about ¼ inchthick) of starch sheet can be used to fabricate padded envelopes orother mailing containers.

[0167] All of the references cited in this specification areincorporated in their entirety by reference herein.

[0168] Those of ordinary skill in the art will appreciate that variants,alternatives, substitutes and equivalents of the devices, methods,techniques, expedients, and ingredients specifically described hereinmay exist and that all such variants, alternatives, substitutes andequivalents that can be employed or readily adapted in the methods andcompositions of this invention are within the spirit and scope of thisinvention which is defined by the appended claims.

We claim:
 1. A method for producing a shaped expanded starch articlewhich comprises the steps of: a. introducing an extruder feedcomposition comprising from about 70% to about 97% by weight starch intoa twin-screw extruder; b. extruding said composition through a die togenerate an extrudate having cells; and c. applying pressure to saidextrudate to substantially compress the cells in said extrudate.
 2. Themethod of claim 1 wherein pressure is applied by rolling said extrudate.3. The method of claim 2 further comprising the step of shaping saidrolled extruded starch by pressure molding.
 4. The method of claim 3wherein said shaped article is a tray.
 5. The method of claim 1 whereinpressure is applied by rolling and said rolled extrudate is alsostretched.
 6. The method of claim 5 further comprising the step ofshaping said rolled, stretched starch extrudate by pressure molding. 7.The method of claim 6 wherein said article is a tray.
 8. The method ofclaim 1 wherein pressure is applied to said extrudate while it is hot.9. The method of claim 1 wherein said starch is predominatelynon-modified starch.
 10. The method of claim 1 wherein said starch isnon-modified starch.
 11. The method of claim 1 wherein said extruderfeed composition comprises less than 5% by weight of a polyolplasticizer.
 12. The method of claim 11 wherein said extruder feedcomposition comprises less than about 2.5% by weight of a polyolplasticizer.
 13. The method of claim 11 wherein said extruder feedcomprises less than 5% by weight of polyvinyl alcohol.
 14. The method ofclaim 1 wherein said extruder feed further comprises a nucleating agent.15. The method of claim 14 wherein said extruder feed further comprisesa lubricant.
 16. The method of claim 15 wherein said extruder feedfurther comprises a humectant.
 17. The method of claim 15 wherein saidextruder feed further comprises a blowing agent.
 18. The method of claim1 wherein said extruder feed further comprises proteinaceous grain meal.19. The method of claim 1 wherein said extruder feed comprises one ormore different types of starch.
 20. The method of claim 1 wherein saidextruder feed further comprises glycerin monostearate.
 21. The method ofclaim 1 wherein said extruder feed comprises rice flour.
 22. The methodof claim 21 wherein said extruder feed comprises a mixture of starch andrice flour.
 23. The method of claim 1 wherein said extruder feedcomprises recycled expanded compressed starch.
 24. The method of claim 1wherein said the starch in said extruder feed is 20% or less by weightrecycled expanded compressed starch.
 25. The method of claim 23 whereinsaid starch in said extruder feed is 10% or less by weight recycledexpanded compressed starch.
 26. The method of claim 1 wherein saidextruder composition further comprises talc.
 27. The method of claim 1wherein sufficient pressure is applied to said extrudate tosubstantially crush the cells in said extrudate.
 28. The method of claim1 further comprising a step of stretching said extrudate before, afteror at the same time it is compressed.
 29. The method of claim 28 whereinsaid extrudate is compressed and stretched at the same time.
 30. Amethod for producing a shaped expanded starch article which comprisesthe steps of: a. introducing an extruder feed composition comprisingabout 70% to about 95% by weight starch into a twin-screw extruder; b.extruding said composition through a die to generate an extrudate havingcells; and c. stretching said extrudate as it emerges from said die. 31.The method of claim 30 wherein said extrudate stretched by pulling itfrom said die at a rated faster than the rate of extrusion.
 32. Themethod of claim 31 wherein said extrudate is stretched at a rate up toabout 1.5.
 33. The method of claim 31 wherein said extrudate isstretched at rate ranging from about 1.1 to about 1.2.
 34. The method ofclaim 30 wherein said starch is predominantly non-modified starch. 35.The method of claim 30 wherein said starch is non-modified starch.
 36. Amethod of pressure molding a shaped expanded starch article whichcomprises the steps of: a. introducing an extruder feed compositioncomprising from about 70% to about 97% by weight starch into atwin-screw extruder; b. extruding said composition through a die togenerate an extrudate having cells; c. applying sufficient pressure tosubstantially compress the cells in said extrudate; and d. introducingsaid compressed extrudate into a pressure mold and thereafter applyingsufficient pressure thereto to form said shaped expanded starch article.37. The method of claim 36 wherein said compressed extrudate is formedinto a sheet.
 38. The method of claim 37 wherein said compressedextrudate sheet is produced by rolling said extrudate.
 39. The method ofclaim 36 wherein said article is a tray.
 40. The method of claim 37wherein said compressed extrudate sheet is produced by rolling andstretching said extrudate.
 41. An extruder feed composition consistingessentially of the following components: non-modified starch in anamount ranging from about 70% to about 97% by weight; proteinaceousgrain meal in an amount ranging from 0% up to about 10% by weight; talcin an amount ranging from 0% up to about 10% by weight; and a blowingagent in an amount ranging from 0% up to about 1.5% by weight, with theproviso that the extruder feed composition must contain a nucleatingagent.
 42. The extruder feed of claim 41 wherein talc is present in anamount ranging from about 1% up to about 10% by weight.
 43. The extruderfeed composition of claim 41 wherein talc is present in an amountranging from about 1% to about 5% by weight.
 44. The extruder feed ofclaim 41 which contains no proteinaceous grain meal.
 45. The extruderfeed composition of claim 41 wherein the proteinaceous grain meal iscorn meal.
 46. The extruder feed composition of claim 41 wherein saidstarch is a mixture of starches from different plant sources.
 47. Theextruder feed composition of claim 41 wherein said non-modified starchis cornstarch.
 48. The extruder feed composition of claim 41 whereinsaid starch comprises rice flour.
 49. A shaped expanded starch articleproduced by the method of claim
 1. 50. An expanded starch sheet producedby the method of claim
 1. 51. A molded expanded starch article producedby pressure molding of the expanded starch sheet of claim
 50. 52. Ashaped expanded starch product produced by the method of claim
 28. 53. Ashaped expanded starch article produced by the method of claim 30.